1. Field of the Invention
The invention relates to a system restart circuit and a system restart method thereof, and more particularly, to a spontaneous system restart circuit suitable to be implemented in a portable electronic device and a spontaneous system restart method thereof.
2. Description of the Prior Art
FIG. 1 is a diagram of a conventional power processing circuit of a portable electronic device such as a notebook, portable multimedia player, cell phone or handheld gaming device. If the microprocessor 10 crashes, a user can stop the device by pressing the restart switch 12. At this time, the BJT 14 is off and the source-to-gate voltage (VSG) of FET 16 is lower than the turn-on voltage of the FET 16 so that the FET 16 turns off, and the current supplied from the power VBAT cannot flow into the system power supplying circuit 18, which causes the device to stop operating. If the user wants to restart the device, he/she must press a power on/off switch (not shown) in order to input a PW ON/OFF enabling signal from node A to turn on the BJT 14, so the FET 16 can establish a channel to conduct the current into the system power supplying circuit 18 once more. Therefore, the conventional power processing circuit of FIG. 1 cannot automatically accomplish the restart process with one restart switch.
Generally speaking, the system restart mechanism includes a hardware restart mechanism and a software restart mechanism. Because the size of a portable electronic device is expected to be small and thin, the portable electronic device is usually unable to provide a hardware restart function, and must executes the restart process by software. For example, a specific command can be preset in a handheld device, and the specific command is executed through an operating interface to restart the device if needed. However, when the software or the microprocessor of the handheld device also crashes, the specific command cannot be executed. The user can only force the device to turn off and then restart by cutting off the power supply of the device (for example, unloading the battery). This not only wastes time but also causes damage to the inner circuit of the device; in other words, it is not convenient to the user.
Additionally, a power restart circuit of a notebook shown in FIG. 2 is proposed. When the restart switch 20 is pressed, the input voltage level of the peripheral device controlling unit 22 changes, and this change will further trigger the peripheral device controlling unit 22 to transmit a power on signal to the power supplying unit 24 to restart the notebook. Therefore the user can restart the notebook by pressing the power restart circuit instead of cutting off the power of the notebook. The drawback of this circuit is its complex structure, which requires the FET 26 and the pulse width modulation (PWM) unit 28, increasing the production cost accordingly.